Packaging method for applying shrinkable covers



mamam& METHOD FOR APPLYING SHRINKABLE COVERS Filed Feb. 7, 1963 T. E. FORD June 28, 1966 3 Sheets-Sheet 1 N EL zC7/Acc97Aco97///// mwgw &O

PACKAGING METHOD FOR APPLYING SHRINKABLE COVERS PACKAGING METHOD FOR APPLYING SHRINKABLE COVERS T. E. FORD June 28, 1966 3 Sheets-S'neet 3 Filed Feb.

United States Patent O 3,257,769 PACKAGING METHOD FOR APPLYING SHRINKABLE CDVERS Thomas E. Ford, Arlington, Mase., assigor to W. R.

Grace & Co., Duncan, S.C., a corporation of Connecticut Filed Feb. 7, 1963, Ser. No. 256343 4 Claims. (Ci. 53-42) This invention relates to an automatic .machine for applying covers to pies, pans of raised b iscuits, sliced l-uncheon meats, tray packaged fruits, and vegetables. In an application, Serial No. 81,191, `filed by Willian T. Snow, JI, et al., a machine was disclosed which applies covers to pans, trays, or backing boards containing or supporting such products. The Snow device is not entirely automatic in that the covering film, before scaling, had to be manually placed over the .goods to be packaged. For convenience and brevity, such goods will hereafter be called "pies" and their pans, trays, or supports will hereafter be called pans, and such meaning is intended in thefollowing specification and claims.

The present invention is an improvement upon the Snow device. It provides means automatically to feed the covering film into the correct position to cover the pie, releases the film covering from the conveying means, shrinks the covers into scaling relationship with the rim of the pan and delivers the sealed product as a completed package at the takeoif station. Inasmuch as these means in the preferred example, hereinafter set forth, are designed to be used in conjunction with and in substitution for certain parts of the Snow device, the entire disclosure of the United States application Serial No. 81,191, filed January 6, 1961, now Patent No. 3,l20,728, is incorporated herein by reference.

The improvement by which the automatic functioning of the pie covering machine can be secured depends upon the discovery that films which have high shrink energy can be gr-ipped frictionally at their lateral margins and that when such a film is subjected to heat in areas adjacent to those margins, the extreme shrink of the film snaps the sheet out from its frictional engagement and throws the film rather forcibly toward its center. In consequence, it is possible to pinch the film between pairs of upper and lower moving belts, cause these to transport thefilm and lay it in proper position over the pie. Then when hot air, flowing upwards through special, -marginal oven vents, strikes the under surface of the film, the film is heated, shrinks near its lateral margins, pulls itself free of its support and tacks itself beneath the margin of the pie pan adjacent the transverse radius of the pie.

Thereafter, with slight modification, the invention disclosed'by Snow et al. completes the sealing of the cover about the rim of the pie pan.

The primary objects of this invention are to make the scaling and packaging of bakery products and grocery items an entirely automatic procedure and to provide apparatus for such Operations. These and other objects and advantages will become apparent from the specifications and from the accompanying drawings wherein FIGURE 1 is a side elevation of the machine with some parts broken away and certain of the parts in section for better illustration;

FIGURE 2 is a top plan view of the oven openings;

FIGURE 3 is a top plan view of the machine With certain parts broken away for better illustration;

FIGURE 4 is a vertical section of the apparatus taken on line 4-4 of FIGURE 1;

FIGURE 5 is a detal perspective view of the holding and transport belts which apply the covering to the containers;

F 4 3,257,769 [Ce Patented June 28, 1966 FIGURE 6 illustrates the completed, covered pie as it nears the takeoff station; and

FIGURE 7 isa magnified cross section of the overhead pressure belt preferably used in the invention.

The packaging apparatus 10, comprises two (or more) elongated beam members 11 and 12, supported upon a plurality of legs 13-13, five of which are shown in FIGURE l. Two (or more) subsidiary beams 14 and 15, stretch longitudinally between the outside legs and ofi er support for the drive motor 16, and the oven fan and fan housing 17. A foraminous conveyor belt 18, is supported between the beams 11 and 12, and is operatively connected to be driven from the motor 16, or other suitable power source.

A plurality of vertical supports 19, 20, 21 and 22, are Secured to the upper frame members 11 and 12. These are shown in FIGURES l .and 3. D-ive moll 23, which derives its power by connection' between it and the roll 24, of the foraminous belt, is journalled between the supports 19 and 22. Journalled between supports 20' and 21 is a shaft 81 upon which are mounted idler rolls 25 which in turn support a slack running heat resistant belt 26. As :best seen in FIGURE 7, the belt 26 actually is comprised of a wide belt .of hoat-resistant rubber 26a and a narrower belt formed of wire links 26b. The wire belt runs underneath the rubber. It is essentially the same length and is equally slack. Its function is to prevent the exceedingly slackrubber belt from slippng. Inasmuch as both belts run together and act as a unit, they will hereafter be referred to as slack belt 26. The lower flight 27, of the belt is extremely slack. It normally falls into contact with the foraminous belt 18, and so rests and presses upon any article passing between belt 18, and itself.

Journalled in and extending transversely between stanchions at the end of beams 11 and 12 are a pair of drive rolls 28, 29 which secure power from the common power source, eg., motor 16. These rolls drive two pairs of endless carrier belts 33-34 and 33a-34a which run over the ilder rolls 35 and 36 journalled between supports 19 and 22. The carrier belt pairs lie on either side of and thus do not interfere with the travel of the slack belt 26. suitable gears, drive belts, etc. are provided as necessary to drive the foraminous conveyor '18, slack belt 26 and belt pairs 3344, 33a-34a at essentially the same speed and in such manner that the pans, film cover sheet and the slack belt lying thereover travel in the same direction.

Instead of merely placing the pie plate at random on the foraminous belt as in the Snow device, foraminous belt 18 carries at spaced ntervals a number of pie pan holders 37 or jigs each adapted to receive a pie plate.

The jigs 37, are loaded with pies at a loading station 38,

i located at far right end of FIGURE 1. The pie loader is not part of the invention but may be a sweep-arm device p operated by a Geneva cross motion and timed so that a pie is loaded with each arrival of successive jigs at station 38.

A sheet-feed device, not part of this invention, takes sheets from a supply stack located on the right end of the machine and delivers single sheets to the nip between the carrier belt pairs in such a manner that each lateral edge of the sheet is gripped between a pair of carrier belts while the leading and trailing edges of the sheet remain free.

Foraminous belt 18, slack belt 26, and the carrier belt pairs all run at the same surface speed, and since the sheet feeder is timed to insert a sheet in the nip at the proper time sequen ce, a pie on jig 37, and the covering sheet`41, enter the oven together, with the sheet extended above 'and completely oovering each pie (see FIGURE 5).

Pressure shoes 30 and 31, supported from the wall ot the oven (see FIGURE 4) and extending for a distance 3 corresponding to the length of slots 43 and 44 (see FIG- URE 2), create an extra pinchpressure between the inrunning adjacent flights of the belts 33-34 and 33a-34a as the belts move by these slots. Belt tensioning devices such as idlers 39 and 47 (FIGURE 1) may be provided to adjust the bite ;of the belt pairs.

FIGURE 2 shows in detail the openings in the oven floor through which hot air is blown upwards against the under surface of the covering sheet of film. As seen in this figure together with FIGURE 5, the slack belt 26, drapes over the pie and forces the sheet of film 41, into contact with the rim of the pan at the leading and trailing points on its periphery. Consequently, the top of the pie is shielded from heat and only the m-argins of the covering film 41, which are exposed beyond the rim of the pan are heated by the up-flowi-ng hot air. The.

shrinkage which tollows as a consequence of heating, locks the sheet 41, or tacks it under the pan rim at its leading and trailing points.

As the heating continues in the first oven stage, the lateral shrinkage in the eXposed areas rises. Then, as the extra pressure between the belts relaxes, since the belts have now moved beyond the pressure shoes 30-31, the inward pull is now so large that the sheet is pulled toward the center of the oven from between each pair of carrier belts, actually snapping rather forcibly as it leaves their grip. The area which was held between the belts and hence is substantially unshrunk snaps against the pie plate and beneath the rim. The continuing shrinkage shrnks the lateral marginal areas of the sheet, which are now free, into a lock-under or tacking position be- -neath the rim of the pan adjacent its transverse diameter.

The -advance of the carrier then carries the pie to position 2 in the oven where the under side of the sheet is exposed to the air entering through the wide openings 45 and 46. As a consequence of this heating, the entire exposed area of the cover shrinks in under the rim of the pie plate. The carrier then moves the pie over the outlet of the cooling fan 50, and then through the heating oven 48, which directs hot air on the top surface of the covered pie and shrinks the cover 'tightly over its entire extent.

longitudinal stretching to accomntodate the 'air bubble.

Trapped between the pinch rolls, the bubble rides" through the whole length of the extrusion, stretching the polyethylene both lvaterally and longitudinally and simultaneously thinning the extrusion to'filmthickness.

If a round pie isto be covered, square sheets of such material as has been described are preferred, for then, the four corners 'do not entirely disappear into the peripheral seal, but leave four pull tabs 58 (FIGURE 6) which in the case of 8- and 10-inch pies, are large enough to be grasped between the thumb and forefinger. Any one of these may be pulled to loosen and remove the covering.

Save for the oven floor with its special apertures, the general design of the oven follows the re-circulati ng hotair design disclosed in the Snow et al. application. Space must be left between the oven wall and the carrier belts to provide a passage for the upward flow of air between the belts and the oven walls in the initial heating stage. (The air-flow pattern is shown by the arrows in FIG- URE 4.) Thereafter, the air flows upward and escapes through the oven roof vent 51, into the duct 52, which leads to the fan intake 53. From the fan the air is forced upward through the *heating chamber 54, which receves its heat from the electric heating coils 56. From there In order for this equipment to be operative and per-' mit the release of the covering material from between the carrier belts, shrinkable films having high shrink energy are necessary. Such film may include various types of heat-shrinkable, plastic films in thickness between /2 and 5 thousandths of an inch. Among such -m ay be mentioned stretched films of rubber 'hydrochloride, stretched films of Vinylidene chloride polymers, stretched films of polystyrene and films of analogous materials which have the necessary mechanical oharacteristics. But, because of its low cost and of its high tensile strength and very high shrink energy, I prefer to use irradiated polyethylene, which, subsequent to irradiation, has been stretched in both directions at least 350%. Irradiated, biaxially oriented polyethylene has high shrink energy, i.e., from 100 to 500 p.s.i. at 96 C. shrink energy is the force of oontraction at a given temperature When the material is restrained and, more specically, it is the measurable tension in a fully mono-directionally restrained strip of film when the film is heated to the specified temperature.

I thave used, successfully, as the base material of the film Alathon 14, having an average molecular weight of 20,000, a density of 0.914 `and a melt index of 1.8- which has been irradiated to an extent of about 12 megarads and then has been stretched biaxially 350% in both lateral 'and longitudinal directions-the finished thickness of the film was 1 /2 mils. This material possesses :the shrink energy of `about 150 p.s.i. in both directions at 96 C. The irradiation may be accomplished in a conventional manner, e.g., by the use of electron .beam generatDI uh .es the 2,000,000 volt General Elecit .passes into a plenum chantber 55, Where the flow divider 57, directs its flow towards the several apertures in the oven floor, thus comp'leting the circuit.

The remaining path of the pie through the apparatus also follows the Snow et al. design. As soon as the pie leaves the oven, it is bottom-colled by passing over the cold air flow directed through the foraminous belt 18, by the cooling fan 50. cooling chills the peripheral seal and makes it possible for the seal later to Withstand the pull which is developed when the entire pie covering is top-shrunk as the pie passes through the final heating chamber 48.

The apparatus has a high throughput and delivers securely sealed pies and other pan or tray p ackaged products without the need of a special operator.

I claim: I

1. The method of applying a film covering to a pansupported pie which comprises frictionally engaging a sheet of high shrink energy film along its lateral edges, supporting the engaged film over a pie, heating the film along its exposed area adjacent its lateral margins to cause the film to pull free of its frictional engagernent and shrink into tight contact with restricted areas of the pan, then heating the entire area of film exposed beyond the pan margin to shrink the film into sealing engagement with the periphery of the pan, cooling the peripheral seal, and subsequently heating the entire exposed covering to shrink the film against the pie.

2. The method according to claim 1 wherein the heat is first directed against the under side of the sheet in areas adjacent the engaged margins and along the median line of said sheet.

3. The method according to claim 1 wherein the engagement of the film covering with the pan is firstestablished at tack points by directing an upward flow of heated gas against restricted areas of the film and the peripheral seal is completed by the subsequent exposure of the unengaged film to heat.

4. The method of applying a film covering to a pansupported pie which includes engaging at least each lateral margin of a covering sheet of heat-shrinkable film between two frictional engaging elements and thereby supporting the sheet closely above the pie, heating the exposed surface of the sheet adjacent its marginal areas to cause the sheet to shrink transversely-and pull free of its frictional engagement, continuing the heating until the sheet tacks itself under the rim of the pie pan and subsequently heating the remaining exposed areas of the sheet t'o seal the cover about the entire periphery of the pan.

References Cited by the Examner UNITED STATES PAT ENTS FRANK E. BAILEY, Pr'mary Exam'ner. B. S TICKNEY, S. ABEND, A. E. FOURNIER,

Exam'ners. 

1. THE METHOD OF APPLYING A FILM COVERING TO A PANSUPPORTED PIE WHICH COMPRISES FRICTIONALLY ENGAGING A SHEET OF HIGH SHRINK ENERGY FILM ALONG ITS LATERAL EDGES, SUPPORTING THE ENGAGED FILM OVER A PIPE, HEATING THE FILM ALONG ITS EXPOSED AREA ADJACENT ITS LATERAL MARGINS TO CAUSE THE FILM TO PULL FREE OF ITS FRICTIONAL ENGAGEMENT AND SHRINK INTO TIGHT CONTACT WITH RESTRICTED AREAS OF THE PAN, THEN HEATING THE ENTIRE AREA OF FILM EXPOSED BEYOND THE PAN MARGIN TO SHRINK THE FILM INTO SEALING ENGAGEMENT WITH THE PERIPHERY OF THE PAN, COOLING THE PERIPHERAL SEAL, AND SUBSEQUENTLY HEATING THE ENTIRE EXPOSED COVERING TO SHRINK THE FILM AGAINST THE PIE. 